The direction of intended motion of a vehicle is determined by the vehicle driver, typically by the position of the driver's shift lever position. When the driver has the shift lever position in park or neutral, no motion is intended in either forward or reverse. When the driver has the shift lever position in drive, low or manual, the direction of intended motion is the forward direction. When the driver has the shift lever position in reverse, the direction of intended motion is the reverse direction.
Conventional powertrains are typically protected from motion in a direction opposite from the direction of intended motion because an engine cannot make torque while spinning itself backward. The transmission directly connects the engine to the direction of intended motion by providing a linkage to the axles that supports axle torque in the direction of intended motion.
However, on hybrid or fuel cell applications with one or more electric motors, the electric motor can provide torque while spinning in either direction. Therefore, the possibility of propelling the vehicle in the direction opposite of intended motion exists.